1. Field of the Invention
The present invention relates to control method and apparatus for a solenoid operation to drive a control valve used to control an oil pressure in an automatic transmission in which gear shift operations are carried out by clutch and release operations of frictional elements through a control of the oil pressure.
2. Description of the Related Art
The automatic transmission is generally constituted by frictional elements such as a plurality of clutches and brakes which are selectively and hydraulically operated (clutched and released) so that a power transmission route (gear-speed range) of a gear transmission system is determined and the operating frictional element is switched to perform a shift to another gear-speed range. In details, the clutch of a certain frictional element is carried out by raising a working oil pressure on the frictional element and the release of the certain frictional element is carried out by lowering the working oil pressure of the frictional element. Such a control of a working oil pressure as described above is carried out by varying a level of a current inputted to an electromagnetic control valve (a linear solenoid valve) driven by an electric current signal prepared to enable the working oil pressure to be set to an arbitrary value. A current command value is divided into several steps from a minimum value to a maximum value according to an arithmetic operation capability of a control purpose computer. Therefore, a relationship between an oil pressure value (oil pressure command value) set as a value of a working fluid pressure and the frictional element to be clutched or released is formed in a stepwise manner. That is to say, a current to be inputted to the solenoid corresponding to the oil pressure is varied in a stepwise manner.
In order to perform a control over a certain control valve as described above, the following inconveniences occur. That is to say, suppose that the oil pressure of the control valve is varied with an elapse of time and, thereafter, such a control that the oil pressure is maintained constant is carried out. In this case, a variation in a hydraulic (working oil pressure) target value and actual working oil pressure (actual hydraulic or actual oil pressure) is varied in the stepwise manner in accordance with the level of the current signal inputted to its solenoid of the control valve. Hence, the oil pressure command value is shifted in the stepwise manner with respect to the oil pressure target value. In addition, in a case where the oil pressure is maintained constant (shell pressure) and the oil pressure target value indicates an approximate value intermediate between one step of the stepwise current, the oil pressure command value is actually given as an oscillating waveform.
On the other hand, the actual working oil pressure is shifted in a critical damping manner due to a mechanical response delay or due to a viscosity resistance of the working oil. At this time, a time delay, a surge, and a variation (oil vibration) of the working oil pressure occur until the actual working oil pressure has reached to the target value. These phenomena provide causes of shift shock and response delay in a shift operation in the automatic transmission. Especially in a case where one of two frictional elements is clutched while the other frictional element is released so that a shift operation is carried out (this gear shift operation is called a change-over gear shift), an engine racing often occurs due to a deviation in timing of both clutch and release operations of the corresponding two frictional elements.
It is, therefore, an object of the present invention to provide solenoid control method and apparatus for an automatic transmission in which abrupt rise or fall of a waveform of the oil pressure command value is relieved so as to suppress response delay and surge developed on actual oil pressure by filtering a current signal varied in a stepwise manner and to be inputted to a solenoid to drive a control valve of the automatic transmission to achieve a predetermined shift operation.
According to one aspect of the present invention, there is provided a solenoid control method for an automatic transmission, comprising: causing a current signal varied in a stepwise manner to pass through a filter having a predetermined transfer function, the current signal being inputted to a solenoid to drive a control valve by which a working oil pressure on at least one frictional element of the automatic transmission is controlled to perform a predetermined shift operation by reducing the working oil pressure to release the frictional element; and inputting the filter passed current signal to the solenoid to drive the control valve.
According to another aspect of the present invention, there is provided a solenoid control apparatus for an automatic transmission, comprising: a filter process section that causes a current signal varied in a stepwise manner to pass through a filter having a predetermined transfer function, the current signal being inputted to a solenoid to drive a control valve by which a working oil pressure of at least one frictional element of the automatic transmission is controlled to perform a predetermined shift operation by reducing the working oil pressure to release the frictional element; and a current inputting section that inputs the filter passed current signal to the solenoid to drive the control valve.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.